What service is port 25?

Port 25 is the SMTP service. Port 25 is opened by the SMTP server and is mainly used for sending emails. SMTP is an email service built on the FTP file transfer service. It is mainly used to transfer email information between systems and provide notifications about incoming letters. Using SMTP, mail transmission can be realized between processing processes on the same network, and mail transmission between a processing process and other networks can also be realized through a relay or gateway.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

Port 25 is the SMTP service and is used for email sending.

Port 25 is opened by the SMTP (Simple Mail Transfer Protocol) server and is mainly used for sending emails.

SMTP service introduction

SMTP is a protocol that provides reliable and efficient email transmission. SMTP is an email service built on the FTP file transfer service. It is mainly used to transfer email information between systems and provide notifications about incoming letters. SMTP is independent of a specific transmission subsystem and only requires the support of a reliable and orderly data flow channel. One of the important features of SMTP is its ability to transmit emails across the network, that is, "SMTP mail relay". Using SMTP, mail transmission can be realized between processing processes on the same network, and mail transmission between a processing process and other networks can also be realized through a relay or gateway.

Function

SMTP is a set of rules for transmitting mail from a source address to a destination address, and controls how letters are relayed. The SMTP protocol belongs to the TCP/IP protocol suite, which helps each computer find the next destination when sending or relaying letters. Through the server specified by the SMTP protocol, we can send the E-mail to the recipient's server. The whole process only takes a few minutes. The SMTP server is a sending email server that follows the SMTP protocol and is used to send or relay emails sent by users. [3]

SMTP is a protocol that provides reliable and efficient email transmission. It is an email service built on the FTP file transfer service. It is mainly used to transfer email information between systems and provide notifications about incoming letters.

One of the important features of SMTP is its ability to transmit mail across the network, also known as "SMTP mail relay". Using SMTP, mail transmission can be realized between processors on the same network, and mail transmission between a certain processor and other networks can also be realized through a relay or gateway. Mail exchange servers with Domain Name Service (DNS) functionality can also be used to identify the next-hop IP address for transmitting mail.

The process of SMTP sending emails

The working process of SMTP protocol can be divided into the following three processes:

(1) Establish connection: here In the first stage, the SMTP client requests to establish a TCP connection with the server's port 25. Once the connection is established, the SMTP server and client begin to advertise their domain names to each other and confirm each other's domain names.

(2) Mail transmission: Using commands, the SMTP client passes the source address, destination address and specific content of the mail to the SMTP server, and the SMTP server responds accordingly and receives the mail.

(3) Connection release: The SMTP client issues an exit command, the server responds after processing the command, and then closes the TCP connection.

Extended knowledge:

25 port vulnerability

#25 port is open by many Trojan programs , such as Ajan, Antigen, Email Password Sender, ProMail, trojan, Tapiras, Terminator, WinPC, WinSpy, etc. Take WinSpy as an example. By opening port 25, you can monitor all windows and modules running on the computer.

Therefore, if you do not want to set up an SMTP mail server, you can close this port. In the service list of the "Services" dialog box, find the Simple Mail Transport Protocol (SMTP) service, change the service status to "Stop", and change the startup type to "Manual".

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